


SwappedOut

by TaeSkull



Category: Undertale (Video Game)
Genre: Alternate Universe - Underswap, Gen, disbelief, don't know how to tag properly lmao, secerets
Language: English
Status: In-Progress
Published: 2018-04-21
Updated: 2019-02-18
Packaged: 2019-04-25 18:54:49
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 2,947
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14384985
Author URL: https://archiveofourown.org/users/TaeSkull/pseuds/TaeSkull
Summary: Sans had made it.He's done it.He's made a, "reset."But something isn't right.





	1. Chapter 1

**Author's Note:**

  * Inspired by [SwapOut](https://archiveofourown.org/external_works/372402) by Cats. 



"WHY HUMAN...?" Sans said in disbelief. "WHY ARE YOU KEEPING ME HERE? DO YOU WANT ME TO SUFFER...?"

Sans was half crying and half mad.

"URGH, PLAYER, YOU CAN DO THIS "RESET," RIGHT? IF SO, WHY DON'T YOU ALREADY!?"

No one answered.

"FINE..."

Sans walked down the empty hall into the elevator. He passed through the empty Frostland and through the silent Magmafall back into Sunnyside town.

"I KNOW YOU'RE THERE, BEHIND THE ABOVE. LOOKING AT ME."

Sans was staring right into the ceiling.

"YOU... YOU... MEGALOMANIAC. YOU'RE ENJOYING THIS, AREN'T YOU? YOU LIKE SEEING MY FRIENDS AND I SUFFER. YOU GAIN POWER FROM OUR SUFFERING, HUH?"

"W-WELL," Sans said with a cough, "I GUESS THAT'S IT THEN, HUH?"

Sans noticed some space between the house and the trees. It looked like that led to the basement, where his brother told him never to go near.

"SORRY, PAPS..."

Sans climbed down the stairs, while his soul started to crack.

"AGH... THAT HURT, I HAVE TO FIND THAT "STUFF" RIGHT NOW, UH... WHAT DID PAPS CALL IT? DETERMINATION?"

Sans found some blueprints for a strange machine, most likely the one Papyrus was working on. He held up the blueprints, and a small slip of paper fell out. it read, "ᴅᴛ: ᴅʀᴀᴡᴇʀ 5."

Luckily enough, there was a drawer labelled, "ᴅʀᴀᴡᴇʀ 5."

"WHAT IS THIS? THIS LOOKS SIMILAR TO THE THING UNDYNE TOLD ME NOT TO GO NEAR."

Sans remembered that one time where he found himself in the True Lab, and saw those horrifying amalgamations of monsters he could almost recognize. Undyne was there to ward off the amalgamations, and Sans thanked her for it. Undyne told him to don't play with the Determination, or it can melt your body into... _those_. Sans made sure he would never use it if he found Determination.

"SORRY UNDYNE, THIS IS WHY I NEVER MAKE PROMISES."

Sans injected the Determination into his body, and his bones started to shake.

"W-WOAH... THIS STUFF IS REALLY STRONG. I-I HAVE TO G-GET TO THE MACHINE TO P-PULL THE LEVER, T-THIS MIGHT BE MY ONLY CHANCE TO T-TRY AND CHANGE THINGS..."

Sans pulled the lever, then, he woke up, like it was a dream.

"WH... WHERE AM I?"

Sans looked around. This was clearly not his room, but it resembled his room.

"WAIT, WHERE'S MY TRICYCLE BED?? WHY IS THERE A... TRASH TORNADO...?"

Sans looked around and he realized that this was his side of the house. Sans walked out of the room, and saw the tape and stop signs on the other room's door.

"PAPS... WHY DID YOU TAKE MY TAPE AND REPLACE MY NAME WITH YOURS?"

"I'M GOING TO COME IN ON THE COUNT OF THREE, SO YOU'D BETTER BRING EVERYTHING BACK!!"

"ONE..."

"TWO..."

"TWO AND A HALF..."

"TWO AND THREE QUARTERS..."

"...AND THREE!"

Sans runs toward the door, but it slowly opened as he almost bumped into it.

"WHAT THE..."

The room was filled with all the belongings from his room. There was a race car bed, and a bunch of figures from his room.

"NO WAY... PAPS, DID YOU DO THIS...?"

"ACTUALLY, IT'D BE BETTER IF I WENT. I NEED TO BE ON PATROL ANYWAYS..."

Sans walked down the stairs.

"UGH, PAPYRUS... HOW MANY TIMES MUST I ASK YOU TO PICK UP THE SOCK?!?"

"WAIT THIS SOCK HAS... OUR HANDWRITING... BUT... HUH?"

_"SANS! PLEASE PICK UP YOUR SOCK!"_

"ok."

_"DON'T PUT IT BACK DOWN! MOVE IT!"_

"ok."

_"YOU MOVED IT TWO INCHES! MOVE IT TO YOUR ROOM!"_

"ok."

_"AND DON'T BRING IT BACK!"_

"ok."

_"IT'S STILL HERE!"_

"didn't you just say not to bring it back to my room?"

_"FORGET IT!"_

"NO... THESE ARE... OUR NOTES... BUT SWAPPED? ACK-"

Sans felt a snap. All the memories are coming back.

"WAIT, NO WAY. DID I ACTUALLY RESET...?"

"WAIT WAIT! PAPYRUS!"

"P-PAPYRUS..."

"WHERE AM I? GRILLBY? YOU LOOK LIKE... MUFFET... HUH?"

"WELL, NOW'S NOT THE TIME. I HAVE TO GO FIND PAPS."

Sans ran all the way to the area where he confronted the human. At that moment, he heard something, that sounded similar to his voice. It was different, though, he didn't know how to describe it.

"heya. you've been busy, huh?"


	2. Chapter 2

**Summary for the Chapter:**

> so i just had a party with my friends for my birthday, so that's pretty cool.

"so... i've got a question for you."

 

Something was not right. It wasn't Papyrus's speech. Sans hid behind a tree in a town that's named Snowdin, from the sign that Sans read earlier while running.

 

"do you think, that even the worst person can change?"

 

Sans felt a wave of guilt.

 

"that anyone, can be a good person, if they just try?"

 

"heh heh heh heh... all right. well, here's a better question."

 

"do you wanna have a bad time?"

 

"anyways, let's just get to the point. kids like you should be burning in hell."

 

Sans watched while the other skeleton was fighting the human, for a very long time. It seemed like forever, until Sans heard the sound of sleep.

 

"heh, didja really think you would be able-"

 

Everything went too fast for Sans to figure out.

 

9999999

 

"... so... guess that's it, huh?"

 

"just... don't say i didn't warn you."

 

Sans saw the skeleton stand up.

 

"i'm going to grillby's."

 

Sans watched as the human ran towards Waterfall, a place that Sans did not recognize. Sans ran toward the other bleeding skeleton, and surprised him.

 

"UH, H-HEY BUDDY, LOOKS LIKE YOU'RE UH, BLEEDING?"

 

"huh? who're you?"

 

"ME? I'M THE MAGNIFICENT SANS!"

 

"that can't be right... i'm sans. sans the skeleton."

 

"HUH?? SO YOU'RE ME... BUT NOT ME??"

 

"i guess."

 

"SO, UH, AM I AN ALTERNATE VERSION OF YOU, OR ARE YOU AN ALTERNATE VERSION OF ME?"

 

"dunno, but tibia-honest, it's weird meeting an alternate version of myself."

 

Sans was trying to hold in his anger at the other Sans.

 

"UGH, YOU'RE JUST LIKE PAPYRUS!"

 

"papyrus? he hates my puns."

 

"NO NO, MY PAPYRUS."

 

"oh."

 

"SO, UH, BEFORE Y-YOU BLEED OUT AND TURN TO DUST, UH... DO YOU WANT ME TO SPREAD IT OVER YOU LOVED THINGS, LIKE, A SOCK OR SOMETHING?"

 

"ha ha very funny, if i was strong enough, i'd sock you."

 

"GH, OK BUT SERIOUSLY, DO YOU NEED ME TO DO ANYTHING?"

 

"uh,  just... take care of my- er, our brother, paps."

 

"warn him about the human, promise me, even though we don't really make promises... heh..."

 

"here, take my clothes."

 

"HUH?"

 

"don't tell papyrus about my death, i think it would hurt him too much if he knew..."

 

"WAIT PRETEND TO BE YOU?? WE ONLY JUST MET! I MIGHT NOT BE ABLE TO-"

 

"yes you can, we're sanses, remember?"

 

"we know each other like the back of our bones-"

 

"BUT I'M NOT A SANS LIKE YOU-"

 

"yes you ARE, just don't tell papyrus that i'm DEAD!"

 

"PROMISE ME... you won't... tell him... unless it's necessary!"

 

"OK OK... I GOT IT, I PROMISE."

 

"thank you... i knew i could... believe in myself... ...bro..."

 

Sans stood there, staring at the dust of himself, in the ground, around his clothes. Sans grabbed the clothes.

 

"SO, THE HUMAN IS KILLING HERE TOO... TYPICAL."

 

"I KNEW I'D END UP IN A GENOCIDE TIMELINE, IT'S ALL I'VE EXPERIENCED, EXCEPT FOR WHEN I DIED EARLY. AFTER THAT, PAPYRUS HAS BEEN BLOCKING ALL THE ATTACKS."

 

"BUT... WHEN I FIND THAT HUMAN... I'LL END ALL OF THIS."

**Notes for the Chapter:**

> wowie, i think i'm doing pretty good.


	3. Chapter 3

**Summary for the Chapter:**

> welp it's a new chapter.

Sans held the clothes in his hands.

 

"EW... IT FEELS UNWASHED... UGH... IS THIS HOW PAPYRUS LIVES?"

 

"Well well well this isn't somethin' you see every day!"

 

"HUH?? A FLOWEY??"

 

Sans was confused at the fact that Flowey was using great grammar.

 

"Golly, another Smiley Trashbag! This is gonna get interesting!"

 

"H-HEY, THAT'S KIND OF MEAN-"

 

"Soo... gonna take over for that other Smiley, huh? Wow... that's pretty generous of you!"

 

While Flowey kept blabbing, Sans was thinking to himself.

 

"(DANG... HE'S LIKE THAT TEMMIE BACK AT HOME. WOAH. HE'S NOT REALLY ENCOURAGING ME LIKE TEMMIE DOES."

 

"HEY!! Are you even listening to me!?"

 

"HUH?? OH, YEAH, I'M LISTENING... MY FLOWERY FRIEND."

 

"... Oh. My. God! you're just like Papyrus, aren't you!?"

 

"I AM? HOW SO? PAPS SMOKES."

 

"Eheheh..."

 

"FLOWEY ARE YOU OK?"

 

"Hey, what if Papyrus found out about you pretending to be his brother?"

 

"WHAT DO YOU ME-"

 

"Will Papyrus still treat you like his brother after your  s i c k  l i e s ?"

 

"IF IT'S PAPS I'M SURE-"

 

"But he MIGHT NOT! Think about it! Why didn't you try to save Smiley Trashbag?  You had a bunch of time! Even you're a Sans yourself, you're super fast! You could've swiped him away before the fatal hit! So... why didn't you? Were you scared? Or did you not believe what was happening??"

 

"THERE'S NO WAY I COULD'V-"

 

"AND! If Papyrus knew you were there to save Sans but didn't, what would he think about you?? Letting the  _real_ brother die, surely Papyrus wouldn't forgive you!"

 

"I..."

 

"PPFFFAHAHAHAHAHA!!! You IDIOT, you should see the look on your face!!!"

 

"WHY YOU-"

 

"ALRIGHT, have fun,  _Sans,_ because I sure will!"

 

"B-BYE..."

 

Sans was questioning what just happened. He stared at the ground where Flowey left.

 

"IF PAPYRUS IS ANYTHING LIKE MY BROTHER- ERR, ME, HE'D PROBABLY FORGIVE ME..."

 

Sans walked away, holding the clothes in his hand.

 

"WOW, THAT'S A LITTLE REFRESHING, LOOKS LIKE I DON'T HAVE TO WORRY ABOUT ANY USING TEMMIES HERE, THEY MIGHT EVEN BE NICE HERE."

 

Later...

 

"EW EW EW, HOW DOES HE EVEN WEAR THIS GREASY JACKET EVERY DAY? A-AND, HOW AM I EVEN SUPPOSED TO ACT LIKE HIM, I DON'T REALLY KNOW HIM, EVEN IF HE IS ME..."

 

Sans struggled with the jacket.

 

"UGH, THIS IS A LITTLE COMFORTABLE THOUGH, I SEE WHY PAPS WOULD LIKE IT. WELL, SINCE HE'S LIKE THE PAPS I KNOW, I GUESS I COULD TRY HIM. OH BOY, THIS IS GONNA BE WEIRD..."

 

"ALRIGHT, LEMME TRY..."

 

"nyeheheh... i'm sans. sans the skeleton."

 

"WAIT- HE DOESN'T ADD NYEH TO IT THEN. AAAAH, I REALLY HOPE PAPS COULD FORGIVE ME..."

 

"ANYWAYS, SINCE PAPS STATIONS RIGHT HERE, I SHOULD GO FURTHER INTO SNOWDIN."

 

'HUH... WHERE'S PAPYRUS?"

 

_"S-SANS!! IS THAT YOU? W-WHAT ARE YOU DOING HERE!?"_

 

"oh uh, h-hey papyrus, i thought i'd just stop by before goin' to the station."

 

_"UH, SANS... ARE YOU OK? YOU DIDN'T MAKE ANY SNOW JOKES. LIKE, UH, IT'S SNOW PROBLEM TO CHECK HERE, OR SOMETHING."_

 

"huh, oh, uh, it's fine... i just wanted tibia check up."

 

Sans cringed at his own joke, but for the sake of Papyrus, he tried to withstand it.

 

_"OH MY GOD!!! YOU WERE WAITING FOR THAT, WEREN'T YOU!?"_

 

"i guess, but uh, bro... i really missed you, i though you would've done somethin' stupid."

 

_"I MISSED YOU TOO, SANS. JUST, I JUST, WANTED TO TRY AND HELP THE HUMAN. I THOUGHT THEY COULD CHANGE. SO I CAME OVER HERE TO TALK TO THEM."_

 

"oh. i see why you'd do that."

 

_"YOU DIDN'T THINK THAT WAS STUPID OF ME?"_

 

"nah bro, you're the coolest, i'd never think that."

 

_"AW, THANKS SANS!"_

 

no problem pa- err, bro."

 

Sans hugged Papyrus.

 

_"SO UH, WHAT'S THAT DUST ON YOU? DID SOMETHING HAPPEN WITH THE HUMAN?"_

 

"oh yeah... uh, the snow blinded them while attacking, so they hit the snow instead, and it got on my jacket."

 

_"OH, ALRIGHTY THEN! NYEH HEH HEH! I'M JUST GLAD YOU'RE SAFE... I DON'T KNOW WHAT I WOULD'VE DONE WITHOUT YOU..."_

 

"so uh, are we just gonna stand there, or t-"

 

_"ARE YOU SWEATING?? DID YOU USE ANY MAGICAL ATTACKS YOU CAN'T HANDLE??"_

 

"huh? oh uh, that, it's fine, nothing to strong..."

 

_"THAT HUMAN... THEY TRIED TO TIRE YOU OUT SO THEY CAN STRIKE YOU, HUH?"_

 

"what? nah, why would they-"

 

Sans saw Papyrus's right eye glow for just a few seconds, before it disappeared.

 

_"ANYWAYS, D-DO YOU NEED A HEAL, OR SOMETHING? HERE, LET ME-"_

 

Sans moved out of the way.

 

_H-HEY! I NEED YOU TO STAND STILL! YOU USUALLY ALWAYS DO, YOU LAZYBONES..."_

 

"o-oh, sorry."

 

Papyrus healed Sans.

 

SANS LV 1 HP 10/1

 

_"NYEH HEH HEH! AS EXPECTED OF THE GREAT PAPYRUS! I HAVE MADE YOUR HEALTH HIGHER SANS! THAT MEANS YOU CAN WITHSTAND MORE ATTACKS!"_

 

"thanks, brother."

 

Sans saw a bit of himself in the innocence of Papyrus.Sans did feel a little bit guilty, but he's sure it was for the best not to tell Papyrus.

 

_"NOW, YOU STAY HERE... I NEED TO TEACH A LESSON TO A CERTAIN STUDENT-"_

 

Sans instantly grabbed Papyrus's hand.

 

_"S-SANS, WHAT-"_

 

"hey paps, i don't think you should go near the human. i don't wanna lose you too."

 

Papyrus saw an image of Sans with a slash over his jacket.

 

_"GH-"_

 

"paps? you ok?"

 

_"UH, Y-YEAH, I'M FINE... I-I THOUGHT I JUST SAW SOMETHING..."_

 

_"ANYWAYS, I'LL BE CAREFUL AROUND THE HUMAN. YOU CAN BELIEVE IN ME."_

 

"but paps they might see you-"

 

_'HEY, IT'S FINE, I, THE GREAT PAPYRUS, AM SUPER STEALTHY!"_

 

"yeah but, the human is dangerous-"

 

_"SANS, IT'S FINE, I'LL JUST BELIEVE THAT THEY COULD-"_

 

"but bro. what if they strike you down?

 

_"I'LL JUST PUT MORE BACKBONE INTO IT THEN."_

 

Sans thought he saw his Papyrus, smoking for a quick second, but it faded away, and just Papyrus was there.

 

"o-ok... but what if you get hit?"

 

_"SANS I WILL NOT! DO YOU TRUST ME OR NOT?? LOOK, EVEN TEST MY STRENGTH! GO ON, HIT ME WITH A BONE OR SOMETHING!!"_

 

Sans felt a sinking feeling.

 

"a-alright..."

 

Papyrus embraced himself.

 

"i guess you win."

 

_"EH? YOU'RE NOT GOING TO HIT ME?"_

 

"nah, i wouldn't wanna hurt my bro."

 

_"GHH- ALRIGHT FINE! I WON'T LOOK FOR THE HUMAN!"_

 

"really?"

 

_"YEP! I DON'T WANT TO WORRY MY ONE AND ONLY BROTHER!!"_

 

"you promise?"

 

" _I... I PROMISE..."_

 

Somehow, that quote made Sans sick. He remembered the exact same words from himself as his last dying breath. Sans was not sure if he could take any more of all of this. But, for the sake of his brother and his world, he must try.

 


	4. Chapter 4

**Summary for the Chapter:**

> heyo, it's been a, uh, l o n g while since i've been here, and i just recently came back. so uh, have this!

_"YOU KNOW, YOU LOOK A BIT UH, ENERGETIC, SANS."_

"eh? what're you talkin' about?

 _"I UH, YOU- I..."_ Papyrus started stuttering.

"what's wrong, bro?"

_"NOTHING, IT JUST LOOKS LIKE YOU'RE, DIFFERENT. YOU HAVE NO BAGS UNDER YOUR EYES."_

"oh yeah. i guess so."

_"I'M PRETTY GLAD FOR ONCE THOUGH! ANYWAYS, I THINK YOU SHOULD TAKE A BREAK. I HAVE TO GO REPORT TO UNDYNE ANYWAYS."_

"undyne...?"

Sans was confused on what Papyrus meant by that. He imagined Undyne, the scientist, commanding the Royal Guards.

_"BROTHER? WHY DO YOU LOOK CONFUSED?"_

"...?" Sans was still questioning it.

_"YOU KNOW UNDYNE, RIGHT? THE TALL BLUE COOL FISH GIRL? THE LEADER OF THE ROYAL GUARDS!"_

"uh, yeah, i think i may know someone like that. yeah."

Sans was thinking about Alphys, but if Alphys and Undyne switched places.

_"YOU KNOW, ALTHOUGH YOU DON'T HAVE ANYMORE BAGS, FOR SOME ODD REASON, HMM, YOU DO SEEM A BIT TIRED."_

"nah, it's uh, nothing b-bro."

_"ANYWAYS! I'M GOING TO REPORT TO UNDYNE! BYE, BROTHER!"_

"actually, PAPS!"

_"HM? WHAT IS IT, BROTHER?"_

"i think, uh, i should report to her instead."

_"WELL, ALRIGHT THEN! IF YOU BELIEVE YOU SHOULD INSTEAD, I'LL ALLOW IT."_

"thanks, bro."

 

Sans walked up to Undyne's post. Undyne looked a bit surprised to see Sans.

"What the, SANS?"

"yeah. what's up?"

"I- WHERE'S PAPYRUS?"

"oh he's behind. i'm lettin' him have a break. he looked extremely tired, so i'm here reportin' for him.

"Alright, well, what do you have?"

"alright so, uh..." Sans trailed off.

"the uh, human didn't encounter my bro."

"What?"

"they encountered me instead."

Undyne looked puzzled.

"don't worry, i stopped 'em for a bit in the, uh, shed."

"Alright, well, anything else to report?"

"no."

"Okay well, I just wanted to inform you as well about everything, it's all gone bad. Everything's been screwed, and I really don't lik-"

They both heard rustling.

 "..."

"UNDYNE!"

It was Monster Kid.

"heya, mk."

"Hello Sans and Undyne! How are you two doing?"

Undyne didn't say anything.

"uh, we're doing fine, undyne's a bit worked up about our current situation."

"Oh, that one. Yeah, I know..."

"alright well, see ya, make sure you stay safe, kid."

"Okay!"

"alright, bye."

Monster Kid left the area.

"I'm glad you took care of that easily, Sans."

"thanks, i guess."

"Now, Sans, I need you to make yourself useful for once and tell Alphys about the human invading."

"hey, i'm pretty useful, you know."

Undyne laughed, quietly.

"Yeah yeah, and Papyrus isn't a kid. Anyways, like i was saying, make sure you tell Alphys about evacuating, thanks."

"alright..." Sans grumbled a bit.

"Besides, even if you wanted to help, you could die! I don't want Papyrus seeing his brother dead, that'd really break me. Trust me Sans, I got this."

"you know, somehow, i doubt that-"

"What'd you say?"

"nothing, leader, just, make sure you stay safe."

"Is that implying something?"

"nah, nothin' at all, your majesty."

 

"That was AWESOME!! Yo, did you see the way she was staring at me? You must be SOOOO jealous right now! C'mon, let's go watch her beat up some bad guys!"

Frisk walked out.

 

Sans was at an area with an abandoned quiche and a bench. The Echo Flower echoed, as always.

"I just wasn't ready for the responsibility."

"...WHATEVER. UGH, I HATE THIS. THEY ALL BELIEVE THEY'LL FIGHT BY THEMSELVES. YET, THEY LEAVE, SANS, OUT OF HELPING, BECAUSE HE'S LAZY. JUST LIKE... MY BROTHER..."

"..."

"WOW, IS THIS WHAT MY BROTHER HAS TO GO THROUGH? MAYBE I SHOULDN'T BE AS TOUGH ON HIM AS I AM. AFTER ALL, I GOTTA BE RESPONSIBLE! UGH... I'M GETTING REALLY TIRED OF BEING LAZY. REMEMBER YOUR GOALS, SANS. REMEMBER..."

Sans sat at the bench, mindlessly talking to himself. He still needs to find a way to stop this human.

**Notes for the Chapter:**

> sorry about the random change of the work again, i'm deciding on something similar to this.

**Author's Note:**

> this is my first fanfic, and of course, it's about undertale.


End file.
